UNO R4 WiFi I2C Pins

Official Hardware UNO Family UNO R4 WiFi
1

I am reasonably familiar with Arduino boards and I2C pins but I found the explanation in the UNO R4 WiFi documentation a bit confusing. The documentation says:

The UNO R4 WiFi has one I2C bus which is marked with SCL and SDA. They are shared with A4 (SDA) and A5 (SCL) which owners of previous UNO's are familiar with. The pullups are not mounted on the PCB but there are footprints to do so if needed.

The pins used for I2C on the UNO R4 WiFi are the following:

  • SDA - D18
  • SCL - D19

My questions:

  1. I understand the SDA and SCL pins near the Reset button are connected to A4 and A5. Neither have pullups. What then is the need for two sets of pins for the same function? Could it not lead to someone unknowingly using the marked SDA and SCL as I2C pins and the A4 and A5 as analog pins?
  2. What are the pins being referred to as D18 and D19?

Thanks,
Vikas

2

There are two sets of pins with the same functions so that both functions can be labelled on the board. Yes, it can/does cause confusion

The digital pin numbers range from D0 to D13 but in fact the A* pins can also be referred to as their digital pin name equivalents
A0 = 14, A1 = 15, A2 = 16, A3 = 17, A4 = 18, A5 = 19
hence the reference to D18 and D19 (A4/A5)

3

That makes it perfectly clear. Thank you.